1. Field of the Invention
This invention relates to a security device and a method for securing electrically powered appliances.
Electrically powered appliances such as television sets, video recorders and personal computers are widely used. However, they are prone to theft.
Security devices have been proposed. One such device including an alarm is fitted to an electrical appliance and adapted so that the alarm will remain off provided the appliance is plugged in and switched on to its power source. Once the power is switched off or disconnected the device is adapted so that the alarm is actuated by physical movement of the appliance. This security device suffers from the disadvantage that a stolen appliance is fully operable in a new location. Another security device is disclosed in GB No. 2137391 in which the device consists of a radio transmitter and receiver with an alarm where both the receiver and alarm are attached to an article. If the article is removed beyond a predetermined distance from the transmitter, the alarm is actuated. Within this device, it is difficult to have a precise effective transmission range.
It is an object of this invention to provide an improved security device which either lessens the likelihood of theft of electrical appliances or improves the chance of recovery of such appliances when stolen.
2. Summary of the Invention
Accordingly, in one form this invention provides a security device for an electrical appliance deriving input from an electrically connected external source, the device comprising a receiver-decoder which is adapted and arranged to allow the appliance to operate in its normal mode when the receiver-decoder receives a predetermined code carried via the external source and not to allow the appliance to operate in its normal mode when the predetermined code is not received.
In another form the invention provides a security device for an electrical appliance deriving input from an electrically connected external source, the device comprising an encoder-transmitter for encoding the external source with a predetermined code.
In a further form the invention provides a security device for an electrical appliance deriving input from an electrically connected external source, the device comprising in combination an encoder-transmitter for encoding the external source with a predetermined code and a receiver-decoder which is adapted and arranged to allow the appliance to operate in its normal mode when the receiver decoder receives the predetermined code and not to allow the appliance to operate in its normal mode when the predetermined code is not received.
The invention further provides a method for securing an electrically powered appliance deriving input from an electrically connected external source, the method comprising the steps of encoding the external source with a predetermined code and adapting the appliance so as to operate in its normal mode only when the predetermined code is received from the external source.
The receiver-decoder is preferably physically fitted within or is an integral part of the appliance.
Preferably the electrically powered appliance further comprises an alarm means within the appliance which alarm means is actuated when the predetermined code is not received by the appliance.
In a preferred embodiment the electrically connected external source is an electricity power supply.
In one preferred form the encoder-transmitter is arranged to frequency modulate a carrier signal with a binary digital code and this signal is carried by the electrical wiring in for example a domestic dwelling. The transmitter-encoder is preferably connected to a dwelling's electrical wiring at a place remote from the appliance to be secured, and preferably is concealed in a safe location.
In this specification the phrase "external source" means the source is physically separate from the appliance. Examples, of external sources would be a domestic dwelling's fixed electricity supply, either alternating or direct current; or an antenna for a television or radio receiver. The "external source" is fixed in the sense that it is not readily physically removed. The "input" may be for example electrical power to drive the appliance or a signal received by an aerial for subsequent reception and amplification. The expression "electrically connected" means physically connected through conducting means and not through the air medium.